1. Field of the Invention
The present invention relates to a method for optimizing the performance of a disk drive. More specifically, it involves the determination of the operational spindle rotation rate based on measured servo performance.
2. Description of the Related Art
Disk drives are principal components in the vast majority of computer systems. The drives store information in a non-volatile manner and can be readily written, read, and re-written. Large amounts of information can be stored on disk drives reliably at low cost.
A typical disk drive consists of one or more rigid disks or xe2x80x9cplattersxe2x80x9d that are attached to a spindle. The spindle is attached to a spindle motor that rotates the spindle and the attached platter or platters. The surfaces of the platters comprise a magnetic medium. As the platters rotate, magnetic heads write magnetic transitions to or read magnetic transitions on the medium.
The magnetic storage portion of the disk platters is organized into substantially concentric circular regions. Each circular region is divided into arcuate sectors formed by regular angular wedge-like demarcations around the disk. The magnetic read and write heads are attached to an actuator that moves the head to read or write a particular sector of the platter or platters.
An important metric for the performance of a disk is the amount of time that it takes for the drive to access a particular piece of data on the disk. The disk access time, in turn, is directly affected by the spindle rotation rate of the disk. In general, a higher rotation rate increases data transfer rate performance due to the reduction of spindle latency. However, a higher rotation rate may also result in degraded track follow performance which may adversely affect data transfer performance. In particular, the physical properties of the disk platters, the heads, the spindle, the associated bearings, the motor, and other components of the disk drive limit the ability to operate head disk assemblies in hard drives at extremely high rotation rates. Manufacturing and quality control costs associated with maintaining the tolerances needed to enable operation of an assembled disk drive at a higher spindle rotation rate result in the substantially increased cost of higher rotation rate drives. For example, in conventional disk drive manufacturing, a portion of disk drives are rejected because they can not meet the target operational spindle rate.
A first aspect of the present invention is a method for determining the operational rotation rate for a head-disk assembly that may be incorporated into a fully assembled disk drive. The head-disk assembly comprises a recording head, a rotary actuator, a spindle motor, and a storage medium. The storage medium is coupled to the spindle motor and has an inner circumference and an outer circumference with a magnetic storage portion between the inner and outer circumference. Servo tracks are written to the storage medium to provide positioning information for the read and write heads. A set of position error values are measured while operating the head-disk assembly at a first spindle rotation rate. These position error values are measured by repeatedly reading the servo tracks and comparing the observed position of the servo track to the expected position. The set of position error values are analyzed to generate a position error metric value. An operational spindle rotation rate is selected based on the position error metric value.
Another aspect of the present invention is a disk drive having a rotary actuator, a recording head mounted on the rotary actuator, and a storage medium. The storage medium has a magnetic-storage portion located between the inner circumference and the outer circumference of the storage medium. The disk drive also has a spindle motor that rotates the storage medium. A recorded operational rotation rate based on position error values is measured during testing. The disk drive additionally has a spindle motor rate controller configured to operate the spindle motor at the recorded operational rotation rate.
Another aspect of the present invention is a servo track writer that writes calibration tracks on the storage medium of a head-disk assembly and that determines the operational disk spindle rotation rate. The head-disk assembly has a head for reading and writing to the disk. The head-disk assembly also has an actuator. The servo track writer has a controller, a servo performance measurement circuit, and a spindle rotation rate circuit. The controller processes a clock reference pattern to determine the location of the write element and directs the head to write the servo tracks on the storage medium. The servo performance measurement circuit measures position error values of the servo tracks written on the head-disk assembly and generates a position error metric value. The spindle rotation rate circuit selects an operational rotation rate based on the position error metric value.